Overview of Milk Composition and Quality

Questions and Answers

What percentage of fat is found in cow's milk according to the given definition?

3.25% (correct)

3.0%

4.0%

3.5%

Which of the following is the main component of milk?

Water (correct)

Proteins

Lactose

Fat

What is the primary form of fat found in milk?

Cholesterol

Phospholipids

Sterols

Triglycerides (correct)

Which nutrient makes up around 5% of the composition of milk?

Lactose Signup and view all the answers

The colloidal suspension of proteins in milk primarily consists of which type of proteins?

Globular proteins Signup and view all the answers

Which of the following animal species contributes significantly to milk production in the Mediterranean countries?

Sheep Signup and view all the answers

What type of emulsion is milk classified as?

Oil-in-water emulsion Signup and view all the answers

Which mineral is found in milk, albeit in small quantities?

Calcium Signup and view all the answers

Which microorganism is primarily responsible for souring in milk?

Lactic acid bacteria Signup and view all the answers

What is primarily caused by lactic acid bacteria dropping the pH below 4.6?

Casein precipitation Signup and view all the answers

Which group of microorganisms is associated with gas production in milk spoilage?

Coliform bacteria Signup and view all the answers

What is the most crucial step in controlling psychrotrophs in milk?

Proper cleaning and sanitizing Signup and view all the answers

Which of the following is NOT a recommended practice to control microbial growth in raw milk?

Holding milk at a high temperature Signup and view all the answers

Which organism is commonly associated with proteolysis in spoiled milk?

Streptococcus faecalis var liquefaciens Signup and view all the answers

Which bacteria are primarily responsible for lipolysis in milk?

Achromobacter spp. Signup and view all the answers

What type of soil is primarily found in dairy facilities that must be removed during cleaning?

Minerals and proteins Signup and view all the answers

What is the result of proteinase activity in milk?

Breakdown of milk proteins leading to gelation and bitterness Signup and view all the answers

Which of the following factors is critical for preserving milk quality after it leaves the cow?

Cleanliness and sanitation Signup and view all the answers

Psychrotrophs in milk primarily pose a risk under which condition?

Low, refrigerated temperatures close to 0°C Signup and view all the answers

What effect does a reduction in temperature below the minimum necessary for microbial growth have on microorganisms in milk?

Extends their generation time Signup and view all the answers

Which of the following enzyme activities can lead to rancidity in milk?

Lipase activity Signup and view all the answers

Which of the following Gram-negative bacteria can be found in raw milk that causes spoilage during refrigerated storage?

Pseudomonas Signup and view all the answers

What is a consequence of enzyme activity from psychrotrophs in milk?

Promotion of starter lactic acid bacteria growth Signup and view all the answers

Which of the following substances may be formed when lactose is fermented?

Lactic acid Signup and view all the answers

What is the role of thiocyanate in the LP system for preserving raw milk?

It is necessary for antimicrobial activity. Signup and view all the answers

At what temperature can raw milk be kept for a few days without spoilage when properly preserved?

4°C Signup and view all the answers

What concentration of hydrogen peroxide is recommended to activate the LP system in milk?

10–15 ppm Signup and view all the answers

How long can preserved milk last at 30°C after the addition of thiocyanate and hydrogen peroxide?

7–8 hours Signup and view all the answers

What is the effect of hydrogen peroxide on raw milk's keeping quality?

It may extend the keeping quality by at least 5 hours. Signup and view all the answers

Which factor does NOT influence the effectiveness of hydrogen peroxide as a preservative?

Flavor additives Signup and view all the answers

What is the minimum required concentration of thiocyanate for effective milk preservation?

0.00015% Signup and view all the answers

How do bacteria in milk contribute to the LP system?

They produce small quantities of hydrogen peroxide. Signup and view all the answers

What is the primary purpose of microbial cleaning in dairy operations?

To reduce microbial contaminants on surfaces Signup and view all the answers

Which temperature range is considered effective for hot water sanitation in dairy plants?

76°C–85°C Signup and view all the answers

What is a key factor that limits the effectiveness of chemical sanitizers?

The presence of organic matter Signup and view all the answers

Why is it important to cool milk quickly after it leaves the udder?

To prolong the shelf life and reduce bacteria growth Signup and view all the answers

What is a benefit of low-temperature storage of milk?

It allows for less frequent raw milk collection Signup and view all the answers

In spray cooling, how is the milk kept at a low temperature?

By spraying chilled water onto the outside of the cans Signup and view all the answers

What type of cooler consists of a coil that circulates chilled water to cool the milk?

Immersion cooler Signup and view all the answers

What is the common temperature of milk when it leaves the udder?

37°C Signup and view all the answers

Study Notes

Overview of Milk

Milk is a secretion from female mammals, primarily cows, consumed worldwide.
U.S. Public Health Service defines cow's milk composition: minimum 8.25% milk solids not fat, and 3.25% fat.
Cow's milk represents the majority of milk available for human consumption; sheep and goats also contribute significantly in some regions.

Composition of Milk

Milk is a complex food, mainly consisting of water (dominant), fats (3.9%), proteins (3.3%), lactose (5%), and minerals (0.7%).
Contains over 100,000 molecular species, including vitamins (A, C), enzymes (like lactoperoxidase), and somatic cells.
Four main types of enzymatic activity in milk: lactose fermentation, lipid hydrolysis, protein breakdown, and phospholipase activity affecting fat globules.

Microbial Growth and Quality Preservation

Quality maintenance relies on cleanliness, sanitation, and careful handling post-milking.
High temperatures during milking favor microbe growth; rapid cooling slows this down.
Raw milk can harbor heat-susceptible pathogens and spoilage microorganisms, emphasizing the importance of temperature control.

Psychrotrophic Microorganisms

Psychrotrophs, which can thrive at low temperatures, are problematic for dairy products, leading to spoilage.
Common psychrotrophic organisms include both Gram-negative (e.g., Pseudomonas) and Gram-positive bacteria (e.g., Bacillus).

Types of Spoilage in Milk

Souring: Caused by lactic acid bacteria.
Casein precipitation: Occurs when pH drops below 4.6.
Gas production: Driven by Clostridium and Bacillus.
Proteolysis and lipolysis: Result from several spoilage bacteria, notably Pseudomonas.

Prevention and Control Measures

Cleaning and Sanitizing: Essential for maintaining milk quality, reducing psychrotroph counts.
Cooling Techniques: Immediate reduction of temperature after milking is crucial; methods include spray and immersion cooling.
Hydrogen Peroxide and Lactoperoxidase Systems: Used in specific conditions to extend shelf life, particularly in regions lacking refrigeration.
- Ideal concentrations include 10-15 ppm of thiocyanate and 300-800 ppm of hydrogen peroxide for preservation.

Summary of Antimicrobial Measures

Maintaining low temperatures significantly extends the storage life of milk.
Use of cleaning agents is critical, with chlorine and iodine-based sanitizers commonly employed in the dairy industry.
Effective sanitation involves both mechanical cleaning and chemical disinfection.

Enzyme Activity Impact

Enzymatic spoilage can lead to undesirable flavor changes and texture alterations in milk, influenced by enzyme-producing microbial activity.
Understanding microbial action on milk is vital for quality control in dairy production.

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Description

This quiz explores the composition of milk, focusing on its nutritional components and microbial quality preservation. It covers the key constituents such as fats, proteins, and vitamins found in milk, as well as the importance of sanitation and temperature control. Perfect for students studying food science or dairy production.